Dialysis system including multi-heater power coordination

ABSTRACT

A dialysis system includes a first fluid heater, a second fluid heater, a supplemental power source and a logic implementer. The logic implementer is configured to use the supplemental power source such that when the first and second heaters are powered simultaneously, a collective current draw does not exceed a maximum allowable current draw of a branch power source powering the system.

PRIORITY

This application claims priority to and the benefit as a continuationapplication of U.S. patent application entitled, “Dialysis SystemIncluding Multi-Heater Power Coordination”, Ser. No. 13/030,909, filedFeb. 18, 2011, now U.S. Pat. No. 8,216,452 B2, which is a continuationapplication of U.S. Ser. No. 12/031,605, filed Feb. 14, 2008, now U.S.Pat. No. 7,892,423 B2, the entire contents of which are incorporatedherein by reference and relied upon.

BACKGROUND

The present disclosure relates generally to medical fluid systems andmore particularly to dialysis systems that can be used in a patient'shome.

It is expected that the power requirements during a typical usage cycleof a home dialysis device will vary significantly. During therapy, whichcan last for two to eight hours, energy usage is expected to beparticularly high. The dialysis delivery and water purification systemsrequire significant amounts of energy to run heaters, pumps, valves,etc. Similarly, disinfection equipment and processes that are operatedat the end of therapy can also require large amounts of electricity. Theinstantaneous amount of energy required during those states may exceedthe wattage which can be supplied by a standard home electrical branch(e.g., 15 ampere, 110/120 volt, or equivalent). The patient's branchpower may need to be upgraded to a higher operating current and/orvoltage to run a therapy.

It is desirable not to have to upgrade the patient's electrical system.

SUMMARY

The system of the present disclosure is a medical fluid system, such asa dialysis system, which can be used in a patient's home. The medicalfluid system in one embodiment generates dialysis fluid. The processbegins by purifying water. The purified water is delivered to thedialysis machine, which adds concentrates to the purified water tocreate dialysate. The apparatus therefore includes a water purificationsystem placed on the front end of the dialysis machine. The systemgenerates dialysate online, that is, it generates the medical fluid asit is needed as opposed to being pre-generated and stored in supplybags. As discussed, the need to upgrade the electrical system of apatient's home to handle both dialysate preparation and dialysatedelivery could provide an impediment to adoption of the therapy. Thepresent system accordingly provides a supplemental power supply, whichis connected in parallel with the patient's line or branch power. Duringtherapy or other high-energy demand operation, the supplemental power isdischarged into the system to prevent the total power draw from the loador branch from exceeding its load rating. After therapy is completed orotherwise when the current requirement of the dialysis system drops, thesupplemental power supply draws power from the branch circuit. Forexample, there may be sixteen to twenty-two hours per day that theequipment is not in use. The supplemental source during this timereplenishes its power reserve for the next dialysis treatment.

In one embodiment, both the branch and the supplemental power devicessupply power during therapy to the dialysis hardware. In variousimplementations illustrated below the branch and the supplemental powerdevices: (i) operate in parallel to supply power to each of the medicalfluid components requiring power; or (ii) are dedicated individually toone or more of the medical fluid components requiring power (e.g.,branch supplies power to each of the medical fluid components requiringpower except for the dialysate preparation unit which is powered via thesupplemental power source). After therapy power from both sources to themedical fluid hardware is shut down (or reduced to a hibernation level),and the line or branch power source recharges the supplemental powersource.

The supplemental power source can be one of several different types,each of which offers different benefits and drawbacks. In oneembodiment, the supplemental power source is an electrochemical batteryor batteries, e.g., which uses a rechargeable chemistry such asLithium-Ion, Lithium-Ion-Polymer, Lithium-Ion-Phosphate, Lithium-Sulfur,Lithium-Nano-Titanate, Nickel-Metal-Hydride, Nickel-Cadmium,Nickel-Iron, Nickel-Zink, Lead-acid, and rechargeable-alkaline cells.Each of the chemistries is capable of storing sufficient amounts ofenergy in a reasonably sized package to fit the medical fluidapplication. These cells are rechargeable but are limited typically toseveral hundred to thousands of charge/discharge cycles before the cellshave to be replaced. Depending on the chemistry of the cells, the cellscan also present environmental issues.

The supplemental power source can alternatively be one or morecapacitor, such as an ultracapacitor (sometimes called asupercapacitor). Ultracapacitors have faster discharge rates than theelectrochemical batteries but offer the benefit of survival acrossmillions of charge/discharge cycles without performance degradation.Moreover, recent advancements in the capacitor field have achievedenergy densities in excess of 300 W(h)/kg, approximately twice thedensity of a Lithium-Ion cell. Moreover, the high rate of discharge forultracapacitor is not necessarily a drawback because the high dischargerate would allow a capacitor of a given energy density to supply moreinstantaneous energy to the system than a battery of equivalent energydensity.

A third option is to convert water during off-therapy hours intopressurized hydrogen using an electrolysis reaction. During therapy, thehydrogen is oxidized in a fuel cell to produce electrical current foruse by the device. The electrolysis reaction is very energy inefficient,however, the resulting hydrogen generation is highly flammable and istherefore stored safely and at relatively low pressures in one preferredembodiment.

For online dialysis, two heaters may be provided, one for a dialysatepreparation unit and one for a dialysate delivery unit. Powering theheaters at both times may exceed the peak current rating for the branchor line power (assuming branch or line power is powering both heaters).The heaters are each powered via a duty cycle using pulse widthmodulation, which for each heater applies maximum power to the heaterfor a first period of time and no power to the heater for a secondperiod of time. The first time relative to the second time sets the dutycycle (e.g., fifty percent duty cycle requires full power for half thetime and no power for half the time).

The present system includes a logic implementer or controller configuredto, as much as possible, apply power to only one of the heaters at anygiven time. For example, the logic implementer or controller can beconfigured such that if the first heater needs power, the logicimplementer looks to see if the second heater is currently beingpowered. If not, the logic implementer causes power to be supplied tothe first heater. If so, the logic implementer keeps checking to see ifthe second heater is currently being powered and causes power to besupplied to the first heater as soon as the second heater is no longerbeing powered. The logic implementer is further configured such that ifthe second heater needs power, the logic implementer looks to see if thefirst heater is currently being powered. If not, the logic implementercauses power to be supplied to the second heater. If so, the logicimplementer keeps checking to see if the first heater is currently beingpowered and causes power to be supplied to the second heater as soon asthe first heater is no longer being powered.

In another example, the logic implementer or controller powers the firstheater for a first predetermined duration and then powers the secondheater for a second predetermined duration, the durations dependent uponthe respective required duty cycles of the two heaters. If thecollective duty cycles are less than one-hundred percent, the logicimplementer or controller is further configured to apply no power toeither heater for a predetermined period of time after one or both ofthe first and second predetermined power durations. In one embodiment,the logic implementer or controller attempts to space apart the poweringof the two heaters as much as possible.

The above algorithms are best suited for first and second heaters thatare sized and configured to each operate at less than fifty percent dutycycle. When the combined duty cycle of the two heaters is greater thanone-hundred percent, the logic implementer is configured to minimize theamount of time of overlapping powering of the first and second heatersas much as possible. To do so, a second heater is powered at the instantpower is removed from a first heater. The logic implementer then waitsas long as possible (according to the duty cycle of the first heater) tore-power the first heater. The second heater is powered for as long asneeded according to its duty cycle. This procedure is repeated,eliminating power overlap as much as possible.

The supplemental power source discussed above can be used to prevent thedual heaters from drawing too much current. In one embodiment, thebranch or line power and the supplemental power source are split to eachpower one of the heaters. In another embodiment, one of the branch orline power alone is used to power both heaters when the heaters do nothave to be powered at the same time. The second power source is calledupon whenever both heaters are being powered, either to power one of theheaters or to add to a collective power source that can provide theneeded current draw of both heaters.

It is accordingly an advantage of the present disclosure to provide amedical fluid system having a relatively large power requirement, andwhich can be used in a patient's home without having to upgrade thepatient's line power.

It is another advantage of the present disclosure to provide a medicalfluid system having a supplemental power source configured to power oneor more electrical component of the system.

It is a further advantage of the present disclosure to provide a medicalfluid system that separates the powering of dual heaters used in thesystem to minimize total power draw.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic view of one embodiment of a medical fluid ordialysis system having a line or branch power source and a supplementalpower source.

FIG. 2 is a schematic view of another embodiment of a medical fluid ordialysis system having a line or branch power source and a supplementalpower source.

FIG. 3 is a schematic view illustrating one mode of operating both theline and branch power sources with the medical fluid or dialysis system.

FIG. 4 is a schematic view illustrating another mode of operating boththe line and branch power sources with the medical fluid or dialysissystem.

FIG. 5 is a schematic view illustrating a further mode of operating boththe line and branch power sources with the medical fluid or dialysissystem.

FIG. 6 is a schematic view illustrating still another mode of operatingboth the line and branch power sources with the medical fluid ordialysis system.

FIG. 7A is a logic flow diagram illustrating one method or algorithm forpowering dual heaters of a medical fluid system.

FIG. 7B is a logic flow diagram illustrating another method or algorithmfor powering dual heaters of a medical fluid system according to amaster/delegate relationship.

FIG. 8 is a logic flow diagram illustrating a further method oralgorithm for powering dual heaters of a medical fluid system.

FIG. 9 is a logic flow diagram illustrating one method or algorithm forpowering dual heaters of a medical fluid system when the two heaterswill at certain times be powered simultaneously.

FIG. 10 is a logic flow diagram illustrating another method or algorithmfor powering dual heaters of a medical fluid system when the two heaterswill at certain times be powered simultaneously.

FIG. 11 is a graph of current draw versus time for dual heaters of amedical fluid system when the total duty cycle for both heaters is lessthan one-hundred percent.

FIG. 12 is a graph of current draw versus time for dual heaters of amedical fluid system when the total duty cycle for both heaters is morethan one-hundred percent.

DETAILED DESCRIPTION Medical Fluid System Having Supplemental PowerSupply

Referring now to the drawings and in particular to FIG. 1, system 10 aillustrates one embodiment of a medical fluid system employing asupplemental power supply or source. System 10 a illustrates a dialysissystem, and in particular an online dialysis system, which producesdialysate or dialysis fluid online (mixing dialysate components at thetime of therapy as opposed to the use of a premixed, bagged dialysate).The dialysis system can be a peritoneal dialysis (“PD”) system, ahemodialysis (“HD”) system, a hemofiltration (“HF”) system, ahemodiafiltration (“HDF”) system and a continuous renal replacementtherapy (“CRRT”) system. System 10 a includes apparatus 12 for receivingline or branch power, such as 120 VAC or 240 VAC residential orcommercial power. Apparatus 12 includes a plug and/or a cord and anyneeded power regulation apparatus, such as a transformer, analog todigital converter and any fusing or other desired circuit protection.

System 10 a includes a supplemental power source or supply 14.Supplemental power source 14 includes wiring or circuit board tracesthat connect to branch power apparatus 12, such that branch powerapparatus 12 can deliver power to supplemental power source 14.Supplemental power supply 14 includes an apparatus capable of receivingpower from branch power apparatus 12, storing such power and deliveringthe power when needed to the medical fluid or dialysis apparatusdescribed herein. The apparatus can be one of several different types,each of which offers different benefits and drawbacks. In oneembodiment, supplemental power source 14 includes an electrochemicalbattery or batteries, e.g., which uses a rechargeable chemistry such asLithium-Ion, Lithium-Ion-Polymer, Lithium-Ion-Phosphate, Lithium-Sulfur,Lithium-Nano-Titanate, Nickel-Metal-Hydride, Nickel-Cadmium,Nickel-Iron, Nickel-Zink, Lead-acid, and rechargeable-alkaline cells.Each of the chemistries is capable of storing sufficient amounts ofenergy in a reasonably sized package to fit the medical fluidapplication. These cells are rechargeable but are limited typically toseveral hundred to thousands of charge/discharge cycles before the cellshave to be replaced. Depending on the chemistry of the cells, the cellscan also present environmental issues.

Supplemental power source 14 is alternatively one or more capacitor,such as an ultracapacitor (sometimes called a supercapacitor).Ultracapacitors have higher faster discharge rates than theelectrochemical batteries but offer the benefit of survival acrossmillions of charge/discharge cycles without performance degradation.Moreover, recent advancements in the capacitor field have achievedenergy densities in excess of 300 W(h)/kg, approximately twice thedensity of a Lithium-Ion cell. A third option is to convert water duringoff-therapy hours into pressurized hydrogen using an electrolysisreaction. During therapy, the hydrogen is oxidized in a fuel cell toproduce electrical current for use by the device.

As discussed, in one embodiment, branch power 12 and supplemental powersource 14 power a dialysis machine 20. In the illustrated embodiment,dialysis machine 20 includes a water purification unit 22, a dialysatepreparation unit 24, a dialysate delivery unit 30 and a disinfectionunit 26. One example of a water purification unit is discussed incopending application Ser. No. 11/937,232, entitled, “Water DistillationSystem For Home Dialysis”, filed Nov. 8, 2007, assigned to the assigneeof the present application, the entire contents of which are disclosedherein by reference. One example of a dialysate preparation unit isdiscussed in U.S. Pat. No. 5,274,434 (“the '434 Patent”), entitled“Method And Apparatus For Kidney Dialysis”, assigned to the assignee ofthe present application, the relevant contents which are incorporatedherein expressly by reference.

Disinfection unit 26 can be part of the dialysate generation anddelivery units, that is, use the same pumps, valves and heater as theother units. Disinfection unit 26 in one embodiment uses the machineheater to heat water within the dialysate circuit to a temperaturesufficient to neutralize infectious agents in the flow path.Alternatively, disinfection unit 26 includes a port for accepting adisinfecting chemical is used with or without heat in the fluid circuit.Disinfection unit 26 further alternatively generates the chemical, e.g.,ozone, which passes atmospheric oxygen through a live electric arc. Theozone is pumped through the dialysate path, sterilizing the path. Toreiterate, disinfection unit 26 can be a separate module, or can useexisting components, which are part of one or more of dialysatepreparation unit 24 and dialysate delivery unit 30.

One example of a dialysate delivery unit 30 is described in the '434Patent above, the relevant portions of which are incorporated expresslyherein by reference. In general, dialysate delivery unit 30 includes acontroller 32, a dialysate heater 34, one or more pump 36 to pumpdialysate (and potentially additionally to pump blood for a blooddialysis treatment), valves 38 and electrically/pneumatically controlledsensors 40, such as pressure sensors, temperature sensors, conductivitysensors, air detection sensors, blood leak detection sensors, etc.

Controller 32 in one embodiment includes a plurality of controllers,each including processing and memory. Controller 32 can for exampleinclude a master or supervisory processor that controls a plurality ofdelegate processors, each of which are dedicated to various functions ofdialysis system 20. Controller 32 can also include redundant processing,such as a safety processor which ensures that each of the otherprocessors is performing its function correctly.

Controller 32 can control any one or more of water purification unit 22,dialysate preparation unit 24 and disinfection unit 26 in addition tocontrolling heater 34, pump 36, valves 38 and sensors 40. In theembodiment illustrated in FIG. 1, controller 32 of dialysate system 20is further configured to control the switching associated with branchpower 12 and supplemental power supply 14 via electrical or signal lines42 a to 42 c, which extend respectively to a branch power switch 44 aconnecting branch power 12 to dialysis machine 20, switch 44 bconnecting branch power 12 to supplemental power supply 14 and a thirdswitch 44 c connecting supplemental power supply 14 to dialysisinstrument 20.

Controller 32 via signal line 42 a selectively opens or closes switch 44a to selectively allow branch power from branch power supply 12 todialysis instrument 20. Controller 32 via signal line 42 b controlsswitch 44 b to allow power selectively from branch power supply 12 tocharge supplemental power supply 14. Controller 32 uses signal line 42 cto selectively open and close switch 44 c to allow supplemental powersupply 14 to supply power to dialysis instrument 20.

In the embodiment illustrated in FIG. 1, branch power supply 12 powerscontroller 32 via a power line 46 independent of switches 44 a and 44 c.In this manner, controller 32 can be powered at anytime via power line46 regardless of the state of switches 44 (referring collectively toswitches 44 a to 44 c). At least a small amount of power can thereforebe supplied to controller 32 of dialysis instrument 20 at any giventime. There may however be instances in system 10 a when no power issupplied to the instrument, e.g., controller 32 runs on on-board batterypower.

Referring now to FIG. 2, alternative system 10 b having branch power 12and supplemental power supply 14 is illustrated. Here, each of thecomponents of dialysis system 20 including water purification unit 22,dialysate preparation unit 24, dialysate delivery unit 30, disinfectionunit 26, branch power apparatus 12 and supplemental power supply 14 arethe same as described above for system 10 a. System 10 b is differenthowever in that a separate controller 50 is provided with supplementalpower supply 14 for controlling switches 44 via signal lines 42(referring collectively to signal lies 42 a to 42 c) to allow (i) branchpower to selectively supply power to dialysis instrument 20 and/orsupplemental power supply 14 and (ii) supplemental power supply 14 toselectively supply power to dialysis instrument 20.

Dialysis preparation unit 30 still includes controller or control scheme32 as described above for controlling any one or more of dialysisdelivery unit 30, water purification unit 22, dialysate preparation unit24 and disinfection unit 26. Separate power line 46 from branch powersupply 12 to controller 32 is not needed in system 10 b. There may beinstances in system 10 b when no power is supplied to the instrument.

In one embodiment, supplemental power supply 14 powers controller 50.Controller 50 can be shutdown at any time dialysis instrument 20 is notfunctioning and no power is supplied from branch power supply 12 tosupplemental power supply 14. Controller 50 is powered and activehowever even if branch power 12, not supplemental power supply 14 issupplying power to dialysis instrument 20 currently.

Regardless of whether system 10 a or 10 b is used, it is contemplated touse a plurality of different switch states for switches 44 to allowpower to be delivered to dialysis instrument 20 (via on or both supplies12 and 14) or for branch power supply 12 to supplemental power supply14. In one switch state, switch 44 b from branch power supply 12 tosupplemental power supply 14 is open, while switches 44 a and 44 c frombranch power 12 and supplemental power supply 14, respectively, todialysis instrument 20 are closed. Here, both power supplies arepowering dialysis instrument 20 and accordingly splitting the overallpower load, so that the overall system 10 (referring collectively tosystem 10 a or 10 b) can operate with existing branch or power in thepatient's home. Different embodiments for splitting the power loadbetween branch power 12 and supplemental power supply 14 are illustratedbelow.

It is contemplated to use only one of branch power 12 and supplementalpower supply 14 when powering dialysis instrument 20, for example, whenthe power load is relatively low. For example, there may be a waterpurification phase in which water purification unit 22, dialysatepreparation unit 24, dialysate delivery unit 30 and disinfection unit 26have to be powered, so that both supplies 12 and 14 are needed. Theremay be a different time during treatment, in which only dialysatepreparation unit 24 and dialysate delivery unit 30 are powered. Hereonly one of the units, e.g., branch power supply 12, needs to powerdialysis instrument 20. Here, switch 44 a is closed, while switch 44 cis open. Switch 44 b can be opened or closed, such that branch power maynot or may, respectively, charge supplemental power supply 14.

Still further alternatively, in the state of therapy in which not asmuch power needs to be delivered, supplemental power supply 14 can bepowering the entire dialysis instrument 20, while branch power 12 iseither not used or is charging supplemental power supply 14. Here,switch 44 c is closed, switch 44 a is open and switch 44 b is open orclosed depending on whether branch power 12 is charging power supply 14.

In another switch state, when therapy is completed, no power is suppliedfrom either branch power 12 or supplemental power supply 14 toinstrument 20 (except perhaps a hibernation load amount of power forexample from branch power 12 to controller 32 via separate power line46). Here, branch power 12 can recharge supplemental power supply 14before the next therapy begins. For example, after eight hours oftherapy using both supplies 12 and 14, system 10 (referring collectivelyto systems 10 a and 10 b) can use the remaining hours of the day, or aportion thereof, to cause branch power 12 to charge supplemental powersupply 14. In such case, switches 44 a and 44 c to dialysis instrument20 are opened, while switch 44 b from branch power 12 to supplementalpower supply 14 is closed. If supplemental power supply 14 becomes fullycharged before therapy begins, switch 44 b can be opened to stop anyfurther charging of supplemental power supply 14.

Referring now to FIGS. 3 to 6, various embodiments for splitting powerbetween branch power 12 and supplemental power source 14 areillustrated. In FIG. 3, branch power 12 and supplemental power source 14are wired into a single pair of power lines 52 a and 52 b to dialysisinstrument 20. Here, the single pair of power lines 52 a and 52 b powersinstrument 20 regardless of the current demand. The lines howeveraccommodate any current demand without having to upgrade branch power12.

Referring now to FIG. 4, a second embodiment for splitting power betweenbranch power 12 and supplemental power source 14 is illustrated. Here,branch power 12 is dedicated to dialysate preparation unit 24, dialysatedelivery unit 30 and disinfection until 26 via branch power lines 54 aand 54 b. Supplemental power source 12 is dedicated to powering waterpurification unit 22 via dedicated supplemental power lines 56 a and 56b. It is expected that water purification unit 22 will consume arelatively high amount of power when it is needed. Supplemental powersource 14 is dedicated to this load. It is also expected thatdisinfection unit 26 will operate at a different time than dialysatepreparation unit 24 is operated.

Further, only a portion of dialysate delivery unit 30, e.g., thedialysate pump or pumps and associated valves, may need to be poweredwhile disinfection unit 26 is running (e.g., to pump hot disinfectingwater or solution from disinfection unit 26 through the dialysate sideof instrument 20 to clean the dialysis instrument. The blood side of ablood treating dialysis treatment may be likewise disinfected or be adisposable unit that does not need to be cleaned. Accordingly, the threeunits 24, 26 and 30 connected to branch power 12 in FIG. 4 will likelynot be operating at least a peak power draw at the same time.

Referring now to FIG. 5, a further alternative splitting of branch power12 and supplemental power supply 14 is illustrated. Here, branch power12 via branch power lines 54 a and 54 b powers dialysate delivery unit30 and disinfection unit 26. Supplemental power supply 14 viasupplemental power lines 56 a and 56 b powers water purification unit 22and dialysate preparation unit 24. Water purification unit 22 anddialysate preparation unit 24 in one embodiment operate in tandem toproduce dialysate or dialysis fluid for use. In an alternativeembodiment, water purification unit 22 operates prior to therapy toproduce purified water. Dialysate preparation unit 24 draws the purifiedwater during treatment to prepare the final dialysate solution.Dialysate delivery unit 30 operates during dialysis to performtreatment. Disinfection unit 26 is used at the end of treatment asdiscussed above to clean dialysis instrument 20. Dialysate delivery unit30 is likely not powered fully while disinfection unit 26 is operatingas discussed above.

Referring now to FIG. 6, yet another alternative embodiment forsplitting power between branch power 12 and supplemental power supply 14is illustrated. Here, branch power 12 via branch power lines 54 a and 54b powers each of water purification unit 22, dialysate preparation unit24 and disinfection unit 26. Supplemental power supply 14 via powerlines 56 a and 56 b is dedicated to powering dialysate delivery unit 30.Here, it is likely that water purification unit 22 and dialysatepreparation unit 24 will be operated at a different time thandisinfection unit 26. Dialysate delivery unit 30 may be powered during aportion or all the time that water purification unit 22, dialysatepreparation unit 24 and disinfection unit 26 are powered. Accordingly,it is believed that the partition of power via FIG. 6 is also anefficient way to split the overall power requirement of system 10.

Multi-Heater Duty Cycle Coordination

It is contemplated that both the water purification unit 22 anddialysate delivery unit 30 will each include a dedicated heater. Heatersare typically one of the larger power consuming components of a medicaldelivery system, including dialysis systems. The heaters can vary from abatch type variety, which typically uses resistive plate heating, to aninline variety, which can use resistive plate heating or inductiveheating (see, e.g., application Ser. No. 11/773,903, entitled “DialysisFluid Heating Systems”, filed Jul. 6, 2007, assigned to the assignee ofthe present application).

The following methods and algorithms partition the individual dutycycles of the dual heaters as much as possible to prevent a combinedpower draw by both heaters from exceeding a current rating of thepatient's line or branch power. It is contemplated to use the followingmethods alone or in combination with the supplemental power supplysystems 10 above to minimize total power draw and to prevent an upgradeof the patient's line or branch power.

Heaters, such as plate heaters, are powered typically via pulse withmodulation (“PWM”). PWM either supplies full power or one-hundredpercent for a certain period of time and then no power or zero percentpower for another period of time. This allows associated electronics tooperate without variable resistors or other type of analog controldevice to apportion full power into some needed percentage. For example,a heater using PWM provides a duty cycle of fifty percent by applyingfull power or one-hundred percent for half the time the heater isoperated and no power or zero percent for the other half of the timethat the heater is operated. In the following examples, the heatersystems and algorithms attempt to modify the PWM sequence to power afirst heater during a second heater's zero percent power or no powerduration and power the second heater during the first heater's zeropower or no power duration.

Method or algorithm 60 of FIG. 7A starts at oval 62 and at diamond 64determines whether a first heater (heater No. 1) needs power. If so,algorithm 60 next determines whether a second heater (heater No. 2) iscurrently being powered at diamond 66. If the second heater is not beingpowered as determined at diamond 66, method 60 causes the first heaterto be powered according to its PWM sequence as seen at block 68. If thefluid heating has not yet been completed, as determined at diamond 70,and if the second heater is not being powered as determined inconnection with diamond 66, method or algorithm 60 makes a return loopto diamond 64 to determine whether the first heater still needs to bepowered. The loop just described is continued until either the systemfinished heating fluid, as determined at diamond 70, or the first heaterno longer needs power, as determined in connection with diamond 64.

If the first heater does not need power, as determined at diamond 64,method or algorithm 60 determines whether the second heater needs powerat diamond 72. If the second heater does need power, a loop back todiamond 64 is created, which continues until either the first or secondheaters needs power. It should be appreciated that during this loopneither heater is powered, which is a time of relatively little currentdraw, which is desirable for reducing the overall load on the associatedresidential or commercial power supply.

When the second heater does need power, as determined in connection withdiamond 72, method or algorithm 60 determines whether or not the firstheater is currently being powered at diamond 74. If the first heater isbeing powered as determined at diamond 74, algorithm 60 returns todiamond 72 to determine whether the second heater still needs power. Theloop between diamond 72 and diamond 74 is continued until the secondheater needs power and the first heater is no longer being powered. Thusit should be seen that method or algorithm 60 prevents the two heatersfrom being heated at the same time and only powers each heater for aslong as it needs to be powered.

When the first heater is no longer being powered and the second heaterneeds power, as determined in connection diamonds 72 and 74, method oralgorithm 60 causes heater number two to be powered according to its PWMsequence as seen in block 76. If the system has not completed its fluidheating, as determined at diamond 70, a loop back to diamond 72 iscreated, which is repeated until either the second heater no longerneeds power or the system has completed its fluid heating. If neitherheater no longer requires power, as determined at diamond 70, method oralgorithm 60 ends as seen at oval 78.

FIG. 7B illustrates a method similar to that of method 60 of FIG. 7A.Here however, method 160 allows for the first and second heaters tooperate in a master/delegate relationship. Here, the master heater isused for any needs of the dialysate preparation unit 24, thedisinfection unit 26 and the delivery unit 30 (e.g., the PD/HD/HDF/CRRTmachine), which is connected to the patient and delivers fluid at aprecise temperature. The delegate heater is assigned to waterpurification unit 22, for which precise control is less critical. Itshould be appreciated that a separate disinfection unit 26 can beprovided for each of PD/HD/HDF/CRRT machine 30 and the waterpurification unit 22 via their own heaters (and/or ozone or chemicals).In such case, the master heater would meet the needs of a firstdisinfection unit 26 for PD/HD/HDF/CRRT machine 30, while the delegateheater would be used to disinfect water purification unit 22.

Water purification unit 22 operates optimally at higher temperatures butdoes not require as precise a control because it has no direct patientconnection. As seen in FIG. 7B, master heater is allowed to heatwhenever needed. Rather than waiting for the delegate heater to finishheating before the master heater begins, system 10 commands the delegateheater to stop heating. The delegate heater then ceases to heat and themaster heater resumes heating. When the master heater is finished,system 10 allows the delegate heater to heat again if needed, until suchtime as the master needs to heat again, causing system 10 to power thedelegate heater down, and so on.

Method or algorithm 160 of FIG. 7B starts at oval 162 and at diamond 164determines whether the master heater needs power. If so, algorithm 160removes power from the delegate heater if it is being heated, as seen atblock 166 and powers the master heater as seen at block 168 (e.g., for aPWM time segment). A loop between diamond 164, block 166 and block 168continues until the master heater no longer needs power as determined atdiamond 164. Algorithm 160 next determines whether the delegate heaterneeds power at diamond 170. If so, algorithm 160 powers the delegateheater at block 172 (e.g., for a PWM time segment). Instead of feedingback to diamond 170 to determine if the delegate heater still needs tobe powered, method 160 returns to diamond 164 to determine if the materheater needs power. If so, the loop between diamond 164, block 166 andblock 168 is begun again and continues until the master heater no longerneeds power as determined at diamond 164. Thus, the heating of thedelegate heater is interrupted as seen at block 166. The loop betweendiamond 164, diamond 170 and block 172 continues until the delegateheater no longer needs power as determined at diamond 170. Method 160 ofsystem 10 then determines if the system should be shut down at diamonded174. If so, method 160 ends as seen at oval 176. If not, the entiremethod is begun again at diamond 164.

Referring now to FIG. 8, method or algorithm 80 illustrates a furtheralternative method or algorithm for controlling the duty cycles of firstand second heaters of a medical fluid treatment, such as a dialysistreatment, so that total power draw at any given time does not exceed amaximum rated power draw for the patient's branch electrical system(residential or commercial). Method or algorithm 80 begins at oval 82,and a first heater of the medical fluid system is powered for apredetermined amount of time (according to its PWM sequence) as seen atblock 84. If the total duty cycle of both heaters is less thanone-hundred percent (e.g., the first heater has a duty cycle offifty-nine percent on and the second heater has a duty cycle of fortypercent), method or algorithm 80 can apportion some or all of theavailable off time and consume a predetermined amount of the off time(no power to either heater) at this point in method 80, as seen at block86.

Method or algorithm 80 then powers a second heater of the medical fluidsystem for a predetermined amount of time (according to its PWMsequence) as seen at block 88. If the total duty cycle of both heatersis less than one-hundred percent, method or algorithm 80 can apportionsome or all of the available off time and consume a predetermined amountof the off time (no power to either heater) at this point in method 80,as seen at block 90.

At diamond 92, method or algorithm 80 determines whether to continueheating (whether fluid heating is completed). If so, the steps taken atblocks 84 to 90 are repeated until heating is no longer required, asdetermined at diamond 92, at which time method or algorithm 80 ends, asseen at oval 94.

Methods or algorithms 60, 160 and 80 of FIGS. 7A, 7B and 8 areparticularly well suited for instances in which the total duty cycle(combined duty cycles of first and second heaters) is less than or equalto one-hundred percent. That is, the percentage of time that the firstheater is powered plus the percentage of time that the second heater ispowered is less than or equal to one-hundred percent. In such case,methods or algorithms 60, 160 and 80 ensure that the heating of oneheater does not overlap the heating of the second heater. Accordingly,the power or current drawn due to the heating of the medical fluidsystem is never greater than the full power or current drawn by eitherheater taken alone.

It should be appreciated that if three heaters (or more) combined forless than a total duty cycle of one hundred percent then method 80, forexample, could be expanded to control three or more heaters withoutexceeding a branch line current or power limit.

FIG. 9 illustrates a method or algorithm 100 which is employed when thetotal duty cycle of both heaters exceeds one-hundred percent. Thismethod or algorithm attempts to minimize as much as possible the timethat the two heaters have to be powered simultaneously. Method oralgorithm 100 begins at oval 102 as illustrated. The first heater ispowered for a predetermined amount of time, as seen at block 104. Thesecond heater is powered at the instant that power is removed from thefirst heater, as seen at block 106. Thus, up to block 106, there is nooverlap in heating. Method or algorithm 100 then determines whether thesystem is to continue heating, as determined at diamond 108. If so,method or algorithm 100 waits as long as possible before powering thefirst heater again based on the duty cycle for the first heater. Theabove loop continues until heating is discontinued, as determined atdiamond 108, after which method or algorithm 100 ends, as seen at oval112.

By waiting as long possible at block 110, method or algorithm 100maximizes an opportunity that the duty cycle of the first heater due toa control algorithm for that heater may be lessened between sequentialapplications of power to the first heater. If the duty cycle of thefirst heater is diminished, method 100 can wait an additional amount oftime before re-powering the first heater, minimizing any overlappingtime that both heaters are powered.

Method or algorithm 100 may be modifies to satisfy a master/delegaterelationship between the heaters. Here, the first or mater heater ispowered as needed. The second or delegate heater is powered for as longas needed but only if the first, master heater is not being heated.Thus, the second, delegate heater may be “starved” of power for certainperiods. Or, the method or algorithm may allow for a small amount ofoverlap, ensuring (i) the first, master heater receives as much power asneeded and (ii) that the overlap does not exceed or overly exceed acurrent or power rating of the patient's or clinic's facility.

FIGS. 5 and 6 above show different embodiments for using a supplementalpower source 14 in combination with branch power 12 to separate anddedicate first and second heaters to one of the power sources. Forexample, FIG. 5 shows branch power dedicated to the dialysate deliveryheater, while supplemental power supply 14 is dedicated to the heaterfor the water purification unit. FIG. 6 shows an alternative embodimentin which branch power 12 is dedicated to the water purification heater,while supplemental power supply 14 is dedicated to the dialysatedelivery heater.

Referring how to FIG. 10, method or algorithm 120 illustrates analternative embodiment for incorporating supplemental power supply 14 toensure that the patient's branch power source is not overtaxed at a timethat both heaters have to be powered simultaneously.

Method or algorithm 120 begins at oval 122. The first and second heatersare powered according to their respective duty cycles, as indicated atblock 124. At diamond 126, method or algorithm 120 determines whetherthe current draw is at or approaching a maximum allowable current draw.For example, the method or algorithm 120 could determine at diamond 126whether the current draw is at ninety-five percent of a maximumallowable current draw. If the current draw is not at or approaching themaximum allowable, method or algorithm 120 uses only line power supply12, as seen at block 128. If the current draw is at or approaching amaximum as determined at diamond 126, method or algorithm 120 uses theline power 12 and supplemental power source 14, as seen at block 130.Here, the branch 12 and supplemental power 14 sources can be distributedaccording to any suitable configuration shown in FIGS. 3 to 6.

At diamond 132, method or algorithm 120 determines whether the system isto continue heating. If not, method or algorithm 120 ends, as seen atoval 134. If so, the steps just described are repeated until heating iscompleted.

Referring now to FIG. 11, a graph of current draw verses time showsgraphically how the power is distributed to the first and second heatersin a situation when the total duty cycle of both heaters is less thanone-hundred percent. Here, a gap g exists in time between each power-onsequence for either the first and second heaters. Here, the total timethat both heaters are on is less than one-hundred percent of the time.Accordingly, the powering of the first and second heaters is spacedapart as much as possible, so that power draw from the line 12 or branch14 power supplies has a rest period before the powering of eitherheater.

In an alternative embodiment, the second heater is powered at theinstant the first heater is switched de-powered, creating a larger timegap g between the time that the second heater is powered and the timethat the first heater is powered.

Referring now to FIG. 12, algorithm 100 of FIG. 9 is illustratedgraphically. Here, as an example, both heaters have an individual sixtypercent duty cycle, meaning that each heater needs to be powered forsixty percent of the total time at full power. Thus beginning at everyten time increments and continuing for two time increments, the totalpower drawn is the sum of the power needed by both the first and secondheaters. Here, the second heater is powered at the instant that power isremoved from the first heater. In the example, and assuming the dutycycles of the heaters stay the same, the system waits four time periodsbefore re-powering the first heater, which is the maximum allowable timethat the system can wait before re-powering the first heater accordingto the existing sixty percent duty cycle of the first heater.

If either the duty cycle of the first or second heaters is lessenedduring this waiting period, the overlap in the heating of both heaterssimultaneously can be lessened. For example, if after the first six timeincrements, the duty cycle of the second heater is reduced to fiftypercent, waiting until ten time increments to re-power the first heaterwill allow the overlap in time both heaters are being heatedsimultaneously to a single time increment. In another example, if theduty cycle of the first heater at any time between time increment sixand time increment ten lessens, e.g., changes to fifty percent, then thesystem can wait until time period eleven before re-powering the firstheater, thus reducing or possibly eliminating (e.g., if duty cycle isdecreased to forty percent) the overlap between time period ten and timeperiod twelve.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. A dialysis system comprising: afirst fluid heater; a second fluid heater; a main power source forpowering the system; a supplemental power source; and a logicimplementer configured to use the supplemental power source such thatwhen the first and second heaters are powered simultaneously, acollective current draw does not exceed a maximum allowable current drawof the main power source.
 2. The dialysis system of claim 1, the firstfluid heater powered via the main power source and the second fluidheater powered via the supplemental power source.
 3. The dialysis systemof claim 1, the first and second fluid heaters configured to be poweredby the main power source when the first and second fluid heaters are notpowered simultaneously, the logic implementer configured to use thesupplemental power source when the first and second fluid heaters arepowered simultaneously.
 4. The dialysis system of claim 1, the firstfluid heater a master fluid heater, the second fluid heater a delegatefluid heater.
 5. The dialysis system of claim 1, the logic implementerconfigured to power the first and second heaters using pulse widthmodulation.
 6. The dialysis system of claim 1, the first fluid heaterconfigured to heat a first fluid and the second fluid heater configuredto heat a second, different fluid.
 7. The dialysis system of claim 1,the first fluid heater configured to operate with a dialysis fluidpreparation unit and the second fluid heater configured to operate witha dialysis fluid delivery unit.
 8. The dialysis system of claim 1, whichincludes a third fluid heater, the logic implementer configured to usethe supplemental power source such that when the first, second and thirdheaters are powered simultaneously, a collective current draw does notexceed a maximum allowable current draw for the main power source. 9.The dialysis system of claim 1, the logic implementer configured to usethe supplemental power source when the collective current drawapproaches a percentage of the maximum allowable current draw for themain power source.
 10. The dialysis system of claim 1, wherein at leastone of the first and second fluid heaters is an in-line fluid heater.11. A dialysis system comprising: a water purification unit; a dialysisfluid delivery unit; a main power source; a supplemental power source; alogic implementer configured to use the supplemental power source suchthat when a water purification component of the water purification unitand a dialysis delivery component of the dialysis fluid delivery unitare powered simultaneously, a collective current draw does not exceed amaximum allowable current draw of the main power source.
 12. Thedialysis system of claim 11, which further includes a dialysispreparation unit, and wherein the logic implementer is configured to usethe supplemental power source such that when the water purificationcomponent, dialysis delivery component, and a dialysis preparationcomponent of the dialysis preparation unit are powered simultaneously, acollective current draw does not exceed a maximum allowable current drawof the main power source.
 13. The dialysis system of claim 11, whereinthe water purification and dialysis delivery components are first andsecond heaters.
 14. A dialysis fluid heating method for a dialysistherapy employing a water purification unit and a dialysis fluiddelivery unit comprising: causing a logic implementer to executeinstructions to supplement a main power source with a separate powersource when a current draw limit of the main power source will beexceeded by a collective current draw by the water purification unit andthe dialysis fluid delivery unit.
 15. The dialysis fluid heating methodof claim 14, which further includes powering a dialysis fluidpreparation unit and causing the logic implementer to executeinstructions to supplement the main power source with the separate powersource when the current draw limit of the main power source will beexceeded by a collective current draw by the water purification unit,the dialysis preparation unit and the dialysis fluid delivery unit. 16.A dialysis fluid heating method for a dialysis therapy employing firstand second heaters comprising: causing a logic implementer to executeinstructions to supplement a main power source with a separate powersource when a current draw limit of the main power source will beexceeded by a collective current draw by the first and second heaters.17. The dialysis fluid heating method of claim 16, which includescausing the logic implementer to execute instructions to supplement themain power source with the separate power source when the current drawlimit of the main power source approaches a percentage of the currentdraw limit.
 18. The dialysis fluid heating method of claim 16, whichincludes setting the percentage at ninety-five percent.
 19. The dialysisfluid heating method of claim 16, which includes powering the main powersource and separate power source via pulse width modulation.
 20. Thedialysis fluid heating method of claim 16, which includes powering thefirst and second fluid heaters by the main power source when the firstand second fluid heaters are not powered simultaneously, and using theseparate power source when the first and second fluid heaters arepowered simultaneously.
 21. The dialysis system of claim 11, wherein thedialysis fluid delivery unit includes the logic implementer, and whereinthe logic implementer is configured to control both the dialysis fluiddelivery unit and the water purification unit.
 22. The dialysis fluidheating method of claim 14, which further includes controlling the waterpurification unit through the dialysis fluid delivery unit.